Removal of mercury by magnetic nanomaterial with bifunctional groups and core-shell structure: Synthesis, characterization and optimization of adsorption parameters

Abstract

In this study, a magnetic nanomaterial CoFe2O4@SiO2@m-SiO2-SH/NH2 with bifunctional groups and core-shell structure was successfully synthesised and employed to remove mercury ions [Hg(II)] for enhancing the corrosion resistance of magnetic iron-based nanomaterials. Furthermore, the grafting conditions were improved for amino (NH2) and thiol groups (SH), while increasing the capacity of iron-based adsorbent. The grafting of NH2 and SH was conducted through a relatively safe, mild and facile hydrothermal method at low temperature (353 K) without using any toxic and harmful solvents. Adsorption-related variables including solution pH, adsorbent dosage, initial concentration (C0) and reaction temperature were studied by response surface methodology analysis, wherein maximum adsorption capacity was used as a response variable. The optimal results indicate that the maximum adsorption capacity of 504.34 mg Hg(II)/g was obtained at a pH of 7.2. The magnetic nanoparticles exhibited high adsorption capacity for Hg(II) ions, i.e., 464.7 mg/g, by pseudo-second-order fitting. In addition, the maximum adsorption capacity calculated from Langmuir fitting was 517.4 mg/g at pH 7. Thermodynamic data showed that the adsorption of Hg(II) was endothermic and spontaneous. Moreover, the adsorption capacity of Hg(II) ions still reached over 300 mg/g after five adsorption–desorption cycles. Finally, the probable adsorption mechanism was discussed.